The Pioneer Anomaly

...In October, a European Space Agency panel recommended a space mission to determine whether Anderson had found something that could rewrite physics textbooks. Some cosmologists even speculate the Pioneer Anomaly might help unravel some of the thorniest problems in theoretical physics, such as the existence of "dark matter" or mysterious extra-dimensional forces predicted by string theory.

For public consumption at least, Anderson and his close-knit group of researchers will not permit themselves the luxury of such grandiose speculation. [continued]

The text mentions that one of the possibilities for the slow down is that the extra dimensions of string theory are tugging at the spacecrafts. I would like how this can be, how can extra dimensions have influence in the dynamics of an object
If this explanation holds true, it would be the so desired experimental confirmation of string theory physics

One question is why is this anomalous acceleration detected on distant spacecraft but not on other orbiting bodies?
It may be explained by a clock drift between atomic clock time and ephemeris clock time, the acceleration being approximately the Hubble acceleration, http://arxiv.org/abs/gr-qc/0403013 ap ~ cH.

I've heard that it can be explained by a more massive-than-expected Kuiper Belt. Specifically, dust in the Kuiper Belt. If evenly distributed, the gravitational forces of the individual particles would cancel out and be unnoticable to any object that orbits interior to the Kuiper Belt. But once in the Kuiper Belt or outside the Kuiper Belt, their presence would be felt and would add to the mass of the solar system, slowing down any object in or external to the Kuiper Belt. If this were the case, you would also expect a more subtle slowing by any object that left the plane of the solar system. This is the case with the Ulysses spacecraft. It is experiencing slowdown as well, but not as much as the Pioneers.

I've found this article in which is said that the Pioneer anomaly is due to a Berry phasehttp://arxiv.org/abs/gr-qc/0401014
According to Wikipedia a Berry phase is "a phase acquired by quantum states when subjected to adiabatic processes, resulting from the geometrical properties of the parameter space of the Hamiltonian."

MOND makes a rather poor explanation of the Pioneer anomolies because over the distance in which they are observed the effect should vary by a factor of about one third, but in fact the effect is very constant.

I think a better explanation is likely that the satellites are simply moving through a very sparse sea of dust rather than a true vacuum, and that occassional slight reductions in speed due to collisions with these dust particles explains the effect.

I've seen references to the effect having been detected by analysing Ulysses' orbit ... but haven't ever found a paper on it. This anomaly is particularly maddening ... it's very weak, not reproduced, what's left after lots and lots of other effects are 'subtracted', not easily testable, ...

Okay this is really out there but what if they only appear to be slowing when in fact what is happeneing is somewhat similar to the effects seen in all these experiments where they make EM signals seem to travel faster than light.

If they entered a field of some kind that made the timing seem faster we would believe they were closer than they actually are and calculate them as slowing down...

We know that light travels different speeds in different mediums. If light seems to be transmitted faster in cesium then it stands to reason that some other particles out there might transmit our communication signal that we use to judge the distance with just a little faster.

IE: Maybe it's an illusion and the effect is very explainable with already known phenomena.

Edit: Then again perhaps I should read more before I shoot my mouth off...
In what way is the distance being measured?

MOND makes a rather poor explanation of the Pioneer anomolies because over the distance in which they are observed the effect should vary by a factor of about one third, but in fact the effect is very constant.

I think a better explanation is likely that the satellites are simply moving through a very sparse sea of dust rather than a true vacuum, and that occassional slight reductions in speed due to collisions with these dust particles explains the effect.

But would not that also cause a varying anomalous acceleration? As the spacecraft slowed down in the outer solar system it would need an increasing density of dust cloud to produce the uniform effect, and it would have to be homogeneous with a density that depended only on the distance to the sun.

Nereid, although the anomalous acceleration is tiny at that range it is a reasonable proportion (10-3) of the Newtonian deceleration.

As the effect has been constant and roughly equal to cH, perhaps it is due to a cosmological rather than dynamical effect, e.g. a drift between ephemeris and atomic clock time.

But would not that also cause a varying anomalous acceleration? As the spacecraft slowed down in the outer solar system it would need an increasing density of dust cloud to produce the uniform effect, and it would have to be homogeneous with a density that depended only on the distance to the sun.

Suppose the the density of the dust in the area where the change in velocity is observed (the outer solar system) is more or less uniform. As previously noted the change in velocity is a very small percentage of the total velocity (the effect is on the order of 1 x 10^-8 cm/s^2 IIRC). Even with this effect, the change is velocity over the range where the effect is observed is smaller than the uncertainty in the effect (+/- about 12%).

The amount of decelleration caused by travelling a distance X through a cloud of dust a velocity V is basically proportional to the density of the dust cloud. As long as the density of the dust cloud is largely constant and the velocity change is modest, the change in velocity due to dust collisions per unit time should be largely constant. The dust cloud doesn't have to be more dense.

Perhaps I'm not being clear about what I mean by I dust cloud. I am imagining that the vaccum is not really empty and that say, in every cubic meter of "empty space" there is one speck of dust in the entire region of the outer solar system. The number of specks you hit is proportional to the area your forward profile sweeps in a given time period and the accelleration isn't really "towards the sun" so much as it is "in the opposite direction of your velocity vector".

Perhaps I'm not being clear about what I mean by I dust cloud. I am imagining that the vaccum is not really empty and that say, in every cubic meter of "empty space" there is one speck of dust in the entire region of the outer solar system. The number of specks you hit is proportional to the area your forward profile sweeps in a given time period and the accelleration isn't really "towards the sun" so much as it is "in the opposite direction of your velocity vector".

OK, perhaps we can test this idea!

Since dust is neutral (or, if charged, its path through the solar system not appreciably affected by its charge), the amount of dust striking the Pioneer craft will be the same as the amount of ISM dust hitting the Earth (for the same cross-section) ... well, not really, but as an OOM, perhaps a good place to start.

So, how much dust would be necessary to account for the Pioneer anomaly? How much does this translate to, in terms of tonnes per annum for a random square km of Pacific Ocean (or Antartica)? How does that estimate compare with what's in deep sea cores (or ice cores)?

To re-iterate, we're only interested in OOM for now; if the numbers are vaguely similar (OOM-wise), we might look to refining the estimates.

This could not be replicated by Earth measurements because particles that sparse would burn up in the atmosphere and be indistinguishable from pollution and the Earth is much more massive per particle impacted so the orbital effect would be negligable.

This could not be replicated by Earth measurements because particles that sparse would burn up in the atmosphere and be indistinguishable from pollution and the Earth is much more massive per particle impacted so the orbital effect would be negligable.

A), most ISM dust particles do NOT burn up in the atmosphere; they settle onto the deep ocean floor (actually everywhere, but only there do they comprise a sufficient component to be detected - elsewhere this signal is drowned out)
B), the larger particles which do burn up leave easily detectable meteor trails; analyses of these can give robust estimates of their incidence
C), a number of spacecraft have detected 'micrometeoride' impacts, which can be analysed to calibrate the ISM component
D), and so on ....

I've seen references to the effect having been detected by analysing Ulysses' orbit ... but haven't ever found a paper on it. This anomaly is particularly maddening ... it's very weak, not reproduced, what's left after lots and lots of other effects are 'subtracted', not easily testable, ...

Let's all hope that LISA gets launched on time!

Agreed. Data from the Galileo probe was also anomalous, yet too weak to be definitive. While no single data set seems compelling, the collective data seems strong enough to merit further research. I believe ESA has a project on this in the works. Can't remember the name off the top of my head, but it may be even more exciting than GPB [gravity probe B]. PF people use too many abbreviations.

From this site: "However, the more scientists study gravity and its effects on celestial objects, the more mysteries they seem to uncover. One example is the so-called 'Pioneer anomaly', named after the NASA space probes Pioneer 10 and 11, on which the effect was first noticed. The anomaly was revealed when a number of spacecraft were seen to be affected by an unknown force that slowed them down. The same behaviour has now been detected on NASA's Galileo and the joint ESA-NASA Ulysses spacecraft."

The mechanism I tend to lean toward his radiation pressure from the collision of the solar wind with its own terminus.

Radiation pressure from the solar wind pushs pioneer away from the sun, not towards.

I don't think it's dust because....
It's such an obvious solution. If it were a good candidate, the top scientists would not speculate anything like a break with newton motion, but they have. The top guys reckon there isn't enough dust around
The force is constant. - meaning the space dust would have to be constant density through space, this is unlikely.
The force is directed towards the sun. A force due to friction with dust would be opposite to the velocity of the probe.
And last but not least, the current cosmological model is riddled with errors at galactic scale, so shouldn't be too suprising when a rare error occurs at solar system scale. This top guy, anderson, points out that the mesurement is based on hubble red shift. Then he speculates that light speed might be changing etc... Personally, I think the fact that we're using hubble red shift gives plently of scope for crazy results, since hubble redshift is part of the crazy cosmological physics scene, which is undoubtably mad, what with all that galactic rotation anomaly and what not. That anderson, top guy that he is, speculates on varying light speed, is evidence for this.

Radiation pressure from the solar wind pushs pioneer away from the sun, not towards.

True, but the suggestion is that the effect is caused by an imbalance in the radiation input/output due to internal heat and radio transmissions as well as solar radiation. Although there may well be some, and some thrust from gas leakage, these are not enough to explain the anomaly, only part of it.

meemoe_uk said:

I don't think it's dust because....
It's such an obvious solution. If it were a good candidate, the top scientists would not speculate anything like a break with newton motion, but they have. The top guys reckon there isn't enough dust around
The force is constant. - meaning the space dust would have to be constant density through space, this is unlikely.
The force is directed towards the sun. A force due to friction with dust would be opposite to the velocity of the probe.

All good points.

meemoe_uk said:

And last but not least, the current cosmological model is riddled with errors at galactic scale, so shouldn't be too suprising when a rare error occurs at solar system scale. This top guy, anderson, points out that the mesurement is based on hubble red shift. Then he speculates that light speed might be changing etc... Personally, I think the fact that we're using hubble red shift gives plently of scope for crazy results, since hubble redshift is part of the crazy cosmological physics scene, which is undoubtably mad, what with all that galactic rotation anomaly and what not. That anderson, top guy that he is, speculates on varying light speed, is evidence for this.

Why suddenly rubbish "the top scientists"? Evidence is building that the standard model, which has required a series of 'fixes', (Inflation, DM, DE), needs revising but the general approach has been sound, i.e. to conflate tested theory (GR) with precise observations. (Hubble Deep Field, WMAP, S/N Ia etc.)

Radiation pressure from the solar wind pushs pioneer away from the sun, not towards.

I don't think it's dust because....
It's such an obvious solution. If it were a good candidate, the top scientists would not speculate anything like a break with newton motion, but they have. The top guys reckon there isn't enough dust around
The force is constant. - meaning the space dust would have to be constant density through space, this is unlikely.
The force is directed towards the sun. A force due to friction with dust would be opposite to the velocity of the probe.
And last but not least, the current cosmological model is riddled with errors at galactic scale, so shouldn't be too suprising when a rare error occurs at solar system scale. This top guy, anderson, points out that the mesurement is based on hubble red shift. Then he speculates that light speed might be changing etc... Personally, I think the fact that we're using hubble red shift gives plently of scope for crazy results, since hubble redshift is part of the crazy cosmological physics scene, which is undoubtably mad, what with all that galactic rotation anomaly and what not. That anderson, top guy that he is, speculates on varying light speed, is evidence for this.

Good comments about (solar) radiation pressure and dust.

However, you lost me when you started talking about the 'hubble red shift' - would you mind taking the time to spell this out a bit please? In particular:
- what this 'hubble red shift' is
- how 'the measurement is based on hubble red shift'
- how 'using hubble red shift gives plently of scope for crazy results'

It's OT, but I'm also curious as what relationship you think there is between the 'hubble red shift' and 'that galactic rotation anomaly'.